This invention relates to a rock bolt.
A friction-type rock bolt relies on friction which is generated between at least part of the bolt and a surrounding surface of a hole in which the rock bolt is located, to be effective. The effectiveness of the anchor, provided by the rock bolt, depends on the frictional force which is generated by the interaction of the bolt with the surrounding rock mass and on the length of the rock bolt which extends into solid rock, beyond the rock which is being supported by the rock bolt.
A mechanically-anchored bolt makes use of an expansion unit, at one end of a shank, which is expanded into close contact with a surrounding wall of a hole in which the rock bolt is inserted. A washer is connected to an opposing end of the shank, with the washer bearing on an outer surface of a rock face in which the hole is formed. The effectiveness of this type of anchor is dependent, at least, on the washer being in load-bearing contact with the rock face.
Although friction-type bolts are relatively easy to install they are susceptible to corrosion and, as noted, the effectiveness of this type of bolt depends on the frictional force which is generated.